Field of the Invention
The present invention relates to an imaging device having an image playback function, and a playback device.
Description of the Related Art
If a moving image and a still image can be shot at the same time with one camera, not only can a shooting scene be viewed as a moving image, but also a decisive scene in the moving image can be seen as a still image for fun. This can significantly enhance the values of shot images. Further, if a moving image at a normal frame rate and a moving image at a high frame rate can be shot at the same time with one camera, a specific scene can be switched to a slow-motion moving image to enjoy the image as a high-definition moving image. This can give a viewer an uplifting feeling.
In the meantime, when a phenomenon, so-called jerkiness, like a kind of frame-by-frame advance happens to a moving image played back, it is common that the quality of the moving image is largely degraded. In order to suppress the jerkiness, there is a need to set an accumulation time close to one frame period in a series of shooting processes. In other words, if the frame rate is 30 fps, a relatively longer accumulation time, such as 1/30 second or 1/60 second, will be adequate. Particularly, in such a situation that the attitude of a camera is instable such as a helicopter shot, this setting is important.
On the other hand, since a still image is required to have the sharpness of shooting a moment, there is a need to set a short accumulation time, for example, about 1/1000 second, in order to obtain a stop motion effect. Further, in the case of a moving image at a high frame rate, one frame period is short. Therefore, for example, when the frame rate is 120 fps, a short accumulation time such as 1/125 second or 1/250 second is inevitably set.
Shooting two images at the same time through a single photographic lens, such as a moving image and a still image, or a moving image at a normal frame rate and a moving image at a high frame rate, means that the aperture values used to shooting these images are the same. Even in this case, it is desired that similar levels of signal charge should be obtained in an imaging element while shooting two images in different accumulation time settings to obtain noiseless images having excellent S/N ratios.
Japanese Patent Application Laid-Open No. 2014-048459 discloses an imaging device including a pair of photodiodes having the shape of pupils asymmetric with respect to each pixel. In the imaging device described in Japanese Patent Application Laid-Open No. 2014-048459, the light-receiving efficiency of one of the pair of photodiodes is high and the light-receiving efficiency of the other photodiode is low. Two signals from the pair of photodiodes are used as separate pieces of image data so that the two images can be shot at the same time.
Further, Japanese Patent Application Laid-Open No. 2003-125344 discloses an imaging device that shoots a high-resolution image (an image having a quality enough for viewing as a still image) during moving image shooting, and a method of processing the shot image. Japanese Patent Application Laid-Open No. 2003-125344 teaches that images are reproduced up to a predetermined resolution (high-resolution images up to the same resolution as the moving image) by a progressive method during moving image playback to enable viewing as a moving image, while the high-resolution image is extracted and transferred as a still image in the case of a still image application.
Although such an imaging device capable of shooting two images at the same time as described in Japanese Patent Application Laid-Open No. 2014-048459 can be expected to improve convenience by presenting two images properly, there is no specific mention on a useful presentation method.
Further, Japanese Patent Application Laid-Open No. 2003-125344 does not present a preferred playback mode of switching between the moving image and the still image at arbitrary times.